An engine of a vehicle may be automatically stopped and restarted during the course of vehicle operation to conserve fuel. If the vehicle is operated frequently in stop and go traffic conditions, the engine may be started and stopped more frequently. When the engine is stopped, the engine oil pump pressure is decreased such that the supply of oil to moving engine components such as the engine crankshaft and rods may be reduced. Additionally, during engine restarting engine cylinders may be filled with a relatively large air charge since engine intake manifold pressure can increase toward atmospheric pressure during an engine stop. Consequently, combustion pressures in the engine cylinders may reach higher levels when the engine is being started. As a result of lower oil pressure and higher cylinder pressures, degradation of rotating engine components may increase during engine starting.
Engine starting may also subject portions of a vehicle's driveline to undesirable torque levels if engine speed is not controlled as desired. For example, since torque transmitted through a transmission torque converter increases with increasing input speed to the torque converter, more than a desired amount of engine torque may be transferred to a vehicle driveline if engine speed increases above a threshold engine speed. One way to control engine speed is via spark timing. Retarding spark timing from minimum spark for best torque (MBT) timing can reduce engine output torque, thereby reducing engine speed. Likewise, advancing spark timing from MBT spark timing can reduce engine output torque, thereby reducing engine speed. Advancing spark from MBT timing may provide improved combustion stability as compared to retarding spark timing from MBT timing. However, if spark is advanced further than desired, it may be possible to achieve higher cylinder pressures than is desired. Thus, it may be desirable to limit engine speed via spark advance from MBT; however, control of engine speed via spark advance may also present engine degradation challenges.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: during an engine start and run-up, retarding a spark timing advanced from a minimum spark timing for best torque spark timing in response to output of a sensor exceeding or being less than a threshold level correlated to crankshaft, bearing, or rod degradation.
By retarding spark timing advanced from MBT timing in response to output of a sensor exceeding or being less than a threshold output or level correlated to crankshaft, bearing, or rod degradation, it may be possible to control engine speed and reduce engine degradation during engine starting. For example, a knock sensor may be the basis for determining whether or not an undesirable amount of stress is applied to engine components during engine starting. If output of the knock sensor is greater than a threshold level, spark timing advanced of MBT timing may be retarded to control engine degradation. Further, if output of the knock sensor is less than the threshold level, spark timing advanced of MBT timing may be advanced further to reduce engine speed if engine speed is greater than desired.
The present description may provide several advantages. For example, the approach may improve vehicle drivability when an engine is automatically started by controlling engine speed. Additionally, the approach may reduce engine degradation related to controlling engine speed during engine starting. Further still, the approach may also help to reduce engine emissions via improving engine starting repeatability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.